In Xerography or an electrophotographic process, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the input document. The latent image is developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The charged toner is electrostatically attached to the latent electrostatic image areas to create a visible replica of the input document. The developed image is then usually transferred from the photoreceptor surface to a final support material such as paper and the toner image is fixed thereto to form a permanent record corresponding to the input document.
In a flash fusing Continuous Feed (CF) machine, toner images are prone to cause smudges and finisher contamination problems because of no release oil being applied to the imaged paper to lubricate the contact surfaces (rollers, belts, baffles) in a finisher equipment. The high frictional force causes the toner particles to break off from the marginally flash fused images. An effective solution is to apply lubricating oil, which is functionally similar to a release oil used in roll fusing having a contact nip for applying pressure, to the print sheet after the flash fusing process and before the sheet enters the finisher equipment. To apply lubricating oil an oil dispenser must be portable and retrofitable to an existing CF machine without using software control. For adaptive to a duplex CF printer, an oil dispenser must be able to apply oil to both sides of a sheet.
Flash fusing is a non-contact fusing technology that is widely used in continuous feed machines. It has advantages in wide range of substrate applications and in the transaction printing market. However, without having lubricating oil on the sheet, toner particles in the printed sheets could be easily rubbed off by rollers and belts in a high speed finisher and result in smudges on sheets and contamination problems in the finisher. To increase the fix performance of flash fusing, an effective solution is to apply lubricating oil or wax to the printed sheet after the flash fusing and before entering a finisher. By this means, the oiled sheet is lubricated as is the case for roll fusing that may prevent smudges and finisher contamination problems. A description of flash fusing is provided in U.S. Pat. No. 5,113,223 which is incorporated by reference herein.
This invention deals with an independent oil dispenser for applying oil to two sides of a printed sheet simultaneously. Prior to the description of the present invention, the following briefly describes the prior art patents and existing practice for comparisons. A conventional oil dispenser uses a wick for contacting an oil applicator then the applicator applies fluid to a fuser roll. A wick assembly generally includes two different layers. A first layer in contact with the surface of the fuser member meters precise amounts of release fluid thereon while a second layer in contact with the first layer and an oil reservoir has high release fluid retention capabilities for supplying the first layer with the fluid. In a preferred embodiment, the wick comprises a layer of Teflon which contacts the surface of a fuser roll and a second layer of Nomex which has its underside in contact with an applicator roll. As shown in U.S. Pat. No. 4,309,957 by Swift of Xerox Corporation, a wick is placed above an oil reservoir. This configuration is not directly suitable to an application that requires a wick be positioned at the bottom of the oil reservoir such as is the case for a duplex printer employing flash fusing where oil needs to be applied to both sides of a sheet after the flash fusing process. The Swift patent is concerned with applying release fluid to a fuser roll, not to an applicator roll.
For placing a wick at the bottom of an oil reservoir in a supply tank, U.S. Pat. No. 6,263,182 by Baker of Lexmark International uses piezo elements for moving a diaphragm for closing and opening oil ports to control oil flow by gravity to a wick pad. However, it requires software control to cycle the piezo elements to distribute oil after every predetermined recording sheet passes through the fuser. The system of Baker includes means for dispensing fluid onto a fuser roller and is part of the machine, not a unit like the present invention that can easily be retrofitted into an existing machine.
For reducing finisher contamination and smudges on printed sheets, a wax dispenser unit may be added at the exit of a Continuous Feed machine employing flash fusing. In the flash fusing system, no lubricating fluid is applied to the sheet at the fusing station. In such wax dispenser two dispensing units may be positioned in opposite direction for applying wax to both sides of a web sheet. Each dispensing unit uses a wax block for supplying wax to an applicator brush roll which is in contact with one side of the web sheet. The coating of wax, however, yields an undesirable waxy surface on the web sheet. Also, the wax dispenser uses an independent motor for controlling the applicator speed and the amount of wax on the sheet. An optimized wax rate, however, may require a brush speed that is different from the sheet speed that leads to brush abrading on the imaged sheet. For avoiding abrading on the imaged sheet, the speed of a lubricating oil applicator should be the same as the sheet speed and the dispensing rate should be independently adjustable. Typical continuous paper web feed units including those usable in the present invention are illustrated in U.S. Pat. No. 6,321,650.